Arrangement for the controllable supply of an electric lamp

ABSTRACT

The invention relates to an arrangement for the controllable supply of a lamp which to this end is arranged in series with a controlled semiconductor switching element. According to the invention the control circuit of the semiconductor switching element is equipped with an optoelectronic coupling element. In case of a defect in the control circuit this element prevents the lamp supply voltage from causing damage in this control circuit. In addition the invention provides the possibility of extinguishing the lamp in a simple manner, substantially without a light flash.

United States Patent [191 Luursema et al.

1 1 ARRANGEMENT FOR THE CONTROLLABLE SUPPLY OF AN ELECTRIC LAMP [75] Inventors: Meerten Luursema; Pieter Jan Bolhuis, both of Emmasingel, Netherlands [73] Assignee: U.S. Philips Corporation, New

York, N.Y.

[22] Filed: Apr. 4, 1973 [21] Appl. No.: 347,925

[30] Foreign Application Priority Data Apr. 20, 1972 Netherlands 1. 7205293 [52] U.S. Cl.-' 315/291, 307/311, 315/297,

[51] Int. Cl. H05b 41/36 [58] Field of Search 315/291-297,

[56] References Cited UNITED STATES PATENTS 3,524,986 8/1970 Harnden 307/311 Gilbreath 315/291 Shuey 307/311 Primary ExaminerAlfred L. Brody Attorney, Agent, or Firm-Frank R. Trifari [57] ABSTRACT The invention relates to an arrangement for the controllable supply of a lamp which to this end is arranged in series with a controlled semiconductor switching element.

7 Claims, 1 Drawing Figure PHASE SHIFT NETWORK PAIENIEBnmea m4,

PHASE SHIFT AMPLIFIERS NETWORK ARRANGEMENT FOR THE CONTROLLABLE SUPPLY OF AN ELECTRIC LAMP The invention relates to an arrangement for controlling the supply of an electric energy to an electric lamp in which the lamp is arranged in series with a controlled semiconductor switching element across two input terminals of the arrangement. A control electrode of the controlled semiconductor switching element is connected to a control circuit, said control circuit incorpoating a potential-separating coupling element between a first part of the control circuit which is connected to the control electrode of the semiconductor switching element and another part of the control circuit, the first part of the control circuit being connected to an auxiliary voltage source.

A known arrangement of the kind mentioned above is described, for example, in U.S. Pat. No. 3,351,810. The coupling element in this known arrangement is a transformer whose primary winding is connected to a network for obtaining a variable phase shift. A drawback of this known arrangement is that in the event of a defect between the coupling element and the semiconductor switching element, the occurrence of a relatively high lamp supply voltage across a secondary winding of the transformer might generate, through the primary winding, a voltage across the phase-shifting network which exceeds the voltage for which this network is designed. I

An object of the invention is to obviate or at least mitigate the said drawback. According to the invention an arrangement for controlling the supply of electric energy to an electric lamp includes a controlled semiconductor switching element arranged in series with the lamp across two input terminals of the arrangement and in which a control electrode of the controlled semiconductor switching element is connected to a control circuit. The control circuit incorporates a potentialseparating coupling element between a first part of the control circuit which is connected to the control electrode of the semiconductor switching element and another part of the control circuit, and whereby the first part of the control circuit is connected to an auxiliary voltage source. The invention is characterized in that the coupling element is an opto-electronic coupling element which is arranged in such a manner that it is free from the influence of the light from the electric lamp.

An advantage of an arrangement according to the invention is that the relatively high lamp supply voltage cannot be transferred to the input side of the coupling element, even for dimmers where this supply voltage is present on that side of the coupling element which faces the control electrode of the controlled semiconductor switching element. As a result, in the event of a defect between the coupling element and the controlled semiconductor switching element, control circuit parts on the other side of the coupling element, such as a phase shifting network of a further control circuit likewise connected to this network, also are not damaged.

The prevention of such damage is related to the fact that a transfer can take place in the coupling element of an arrangement according to the invention in one direction only, namely from the light-transmitting part to the photosensitive part.

The light-transmitting part is formed, for example, by an auxiliary incandescent lamp.

In an arrangement according to the invention the light-transmitting part of the opto-electronic coupling element is preferably a light-emitting diode and the photosensitive part of this coupling element is a photosensitive transistor.

An advantage of this preferred embodiment is that the coupling element may be a very compact and cheap structural unit.

It is to be noted that opto-electronic coupling elements are known per se.

The electric lamp of an arrangement according to the invention is, for example, one incandescent lamp. An arrangement according to the invention may alternatively feed, for example, more than one lamp.

In a further preferred embodiment of an arrangement according to the invention, in which the lamp is an inductively stabilized discharge lamp and in which a first switch is present in series with the lamp and with the controlled semiconductor switching element, the control circuit includes a second switch for extinguishing the light from the light-transmitting part of the coupling element.

An advantage of this preferred embodiment is that the arrangement may also be switched off without this being accompanied by a bright lighting up of the lamp. The procedure to accomplish this end is firstly to operate the second switch so that the light-transmitting part of the coupling element is rendered inactive and hence also the control of the semiconductor switching element, and to subsequently open the first switch in series with the lamp.

In a proposed embodiment in which the coupling elemerit is a transformer and in which likewise the first of the two said switches is present, a switching off of this transformer by a subsequent switch (present in the control circuit) results in an instantaneous variation of the control of the controlled switching element such that a troublesome light flash of the lamp often occurs.

When using a transformer coupling element other more complicated methods have to be'used, for example, all control electrodes have to be switched off first before switching off the voltage supply.

A first opening of the first switch in series with the lamp is not to be recommended because then the current from a possible cos d) -capacitor may maintain the relevant semiconductor open for some time so that a light flash would also be produced.

The invention will be further described with reference to the accompanying drawing which shows an electrical circuit diagram of an arrangement according to. the invention.

Input terminals 1 and 2 are intended to be connected to an alternating voltage supply of 220 Volt, 50 Hz. Reference numeral 3 is a two-terminal switch. The terminals beyond the switch 3 are denoted by 4 and 5. A series arrangement of a low-pressure mercury vapour discharge lamp 6 of, for example, 40 Watts, a stabilizing coil (ballast) 7 and two anti-parallel arranged thyristors 8, 9 are connected to the terminals 4, 5. Furthermore a cos b -capacitor 10 for improvement of the power factor and a filament current transformer 11 are connected to the terminals 4, 5. Two secondary windings l2, 13 of the transformer 11 serve to supply the preheatable electrodes of the lamp 6.

Finally, a variable phase-shifting network 14, not shown in detail, is connected to the terminals 4, 5. A resistor B5 is connected to an output terminal of this network 14. The other side of the resistor is connected by two oppositely arranged diodes l6 and 17 to another output terminal of the network 14. A switch 18 (second switch) shunts the diodes l6 and 17.

The diode 16 forms part of an opto-electronic coupling element 19 the photosensitive part of which is a transistor. Likewise the diode 17 forms part of a similar opto-electronic coupling element 20. The terminals of an auxiliary direct voltage source are denoted by 21, and 22 is an amplifier. Conductors of the amplifier 22 lead to the control electrode and to the cathode of the thyristor 8.

Similarly, 23 denotes the terminals of an auxiliary direct voltage source and 24 denotes an amplifier. The amplifier 24 is similarly connected to conductors which lead to the control electrode and the cathode of the thyristor 9.

in the normal situation the lamp 6 is energized when the switch 3 is switched on. The brightness of the lamp 6 is then determined by the phase-shifting network which 14 passes control signals through the optoelectronic coupling elements 19 and to the thyristors 8 and 9..

A defect in a control part between one of the coupling elements (19 or 20) and the relevant thyristors (8, 9) cannot be transferred to the input part of the coupling elements. Thus it is avoided that other parts of the control circuit might be damaged.

When switching off the arrangement the switch 18 is closed first so that the coupling elements 19, 20 are rendered inactive. Subsequently the switch 3 is opened. This process leads to an extinction of the lamp 6 without the accompaniment of a bright flash of light from the lamp.

What is claimed is:

l. A circuit for controlling the supply of electric energy to an electric discharge lamp comprising, a pair of input terminals adapted to be connected to a source of electric energy, a controlled semiconductor switching element, a first switch, means connecting the discharge lamp and the first switch in series with the controlled semiconductor switching element across said pair of input terminals, a control circuit for the switching element, means connecting a control electrode of the controlled semiconductor switching element to said control circuit, said control circuit including a potentialseparating coupling element coupled between a first part of the control circuit which is connected to the control electrode of the semiconductor switching element and another part of the control circuit, means connecting the first part of the control circuit to an auxiliary voltage source, and said coupling element comprises an opto-electronic coupling element including a light-transmitting member and a photosensitive member which is arranged in such a manner that it is free from the influence of the light from the electric lamp, and said control circuit further includes a second switch for selectively extinguishing the light from the light-transmitting member of the opto-electronic coupling element.

2. A circuit as claimed in claim 1, characterized in that the light-transmitting member of the optoelectronic coupling element comprises a light-emitting diode and that the photosensitive member of said coupling element comprises a photosensitive transistor.

3. A system for controlling an electric discharge lamp comprising, a pair of input terminals adapted to be connected to a source of AC voltage, a controlled semiconductor switching element, means connecting the discharge lamp in series with the controlled switching element across said input terminals, a control circuit including a first part having an auxiliary source of voltage connected to a control electrode of the switching element for controlling the current flow therein, said control circuit further comprising an opto-electronic coupling element coupling the first part of the control circuit to a second part of the control circuit that includes means for producing a control signal for operating the opto-electronic coupling element and for controlling the controlled switching element via the first part of the control circuit, said opto-electronic coupling element being disposed so as to be unaffected by the light from said discharge lamp.

4. A system as claimed in claim 3 wherein .said optoelectronic coupling element comprises first and second light emitting diodes connected in anti-parallel to a source of voltage and first and second photosensitive transistors optically coupled to said first and second light emitting diodes, respectively.

5. A system as claimed in claim 3 wherein the control signal producing means of the second part of said control circuit includes a variable phase shift network with input terminals connected to the AC input terminals of the control system for deriving a control signal that varies as a function of the AC supply voltage at said AC input terminals.

6. A system as claimed in claim 5 further comprising a current stabilizing reactance element connected in series with the lamp and the switching element across the system AC input terminals.

7. A system as claimed in claim 3 further comprising a switching device for selectively deactivating the optoelectronic coupling element prior to deenergization of the discharge lamp.

i i k 

1. A circuit for controlling the supply of electric energy to an electric discharge lamp comprising, a pair of input terminals adapted to be connected to a source of electric energy, a controlled semiconductor switching element, a first switch, means connecting the discharge lamp and the first switch in series with the controlled semiconductor switching element across said pair of input terminals, a control circuit for the switching element, means connecting a control electrode of the controlled semiconductor switching element to said control circuit, said control circuit including a potential-separating coupling element coupled between a first part of the control circuit which is connected to the control electrode of the semiconductor switching element and another part of the control circuit, means connecting the first part of the control circuit to an auxiliary voltage source, and said coupling element comprises an opto-electronic coupling element including a light-transmitting member and a photosensitive member which is arranged in such a manner that it is free from the influence of the light from the electric lamp, and said control circuit further includes a second switch for selectively extinguishing the light from the light-transmitting member of the opto-electronic coupling element.
 2. A circuit as claimed in claim 1, characterized in that the light-transmitting member of the opto-electronic coupling element comprises a light-emitting diode and that the photosensitive member of said coupling element comprises a photosensitive transistor.
 3. A system for controlling an electric discharge lamp comprising, a pair of input terminals adapted to be connected to a source of AC voltage, a controlled semiconductor switching element, means connecting the discharge lamp in series with the controlled switching element across said input terminals, a control circuit including a first part having an auxiliary source of voltage connected to a control electrode of the switching element for controlling the current flow therein, said control circuit further comprising an opto-electronic coupling element coupling the first part of the control circuit to a second part of the control circuit that indudes means for producing a control signal for operating the opto-electronic coupling element and for controlling the controlled switching element via the first part of the control circuit, said opto-electronic coupling element being disposed so as to be unaffected by the light from said discharge lamp.
 4. A system as claimed in claim 3 wherein said opto-electronic coupling element comprises first and second light emitting diodes connected in anti-parallel to a source of voltage and first and second photosensitive transistors optically coupled to said first and second light emitting diodes, respectively.
 5. A system as claimed in claim 3 wherein the control signal producing means of the second part of said control circuit includes a variable phase shift network with input terminals connected to the AC input terminals of the control system for deriving a control signal that varies as a function of the AC supply voltage at said AC input terminals.
 6. A system as claimed in claim 5 further comprising a current stabilizing reactance element connected in series with the lamp and the switching element across the system AC input terminals.
 7. A system as claimed in claim 3 further comprising a switching device for selectively deactivating the opto-electronic coupling element prior to deenergization of the discharge lamp. 